Comparison of three distinct methods for the detection of circulating tumor cells in colorectal cancer patients

The detection of circulating tumor cells (CTCs) has considerable utility in the clinical management of patients with solid cancers. However, the phenotypic heterogeneity of CTCs and their low numbers in the bloodstream of patients means that no standardized detection method currently exists for these cells. This, together with differences in pre-analytical sample processing, has led to the collection and accumulation of inconsistent data among independent studies. Here, we compare the ability of three methods to detect CTCs in the blood of colorectal cancer patients. Specifically, different aliquots of the same blood sample were screened for the presence of CTCs by a multimarker RT-PCR assay, the standardized CellSearch assay and dHPLC-based gene mutation analysis. In the population tested, none of the blood samples analysed appeared to be positive by all three methods. Of the samples, 75% were positive for the presence of CTCs by the RT-PCR method. Only 20% were positive by the CellSearch assay, while 14.3% of samples displayed gene mutations consistent with the presence of CTCs when the dHPLC method was applied. The samples which were positive for CTCs by the CellSearch assay did not overlap with those that were positive by dHPLC. Interestingly, however, all of these samples were positive when assessed by RT-PCR. Conversely, of the samples that resulted negative by RT-PCR analysis, none appeared to be positive by either of the other methods. These data, therefore, indicate that of the three methods tested, the multimarker RT-PCR assay provides maximal probability of CTC detection. Here, we present the preliminary results of an ongoing clinical study. Future follow-up involving detection of CTCs in the blood of colorectal cancer patients using these three distinct methods will allow us to verify whether either a single method, or a combination of different assays, is necessary to uncover further prognostic significance of circulating tumor cells.